Expert: Cleggsan - 3/10/2009

Question
QUESTION: hi - I have a stereo powered output and I would like to hook up a mono sub to it. What do you think the best way for me to go about this is? Is there a passive circuit that I can wire up?

ANSWER: ONE: If the stereo amp is bridgeable you can connect the bridged output to the single sub.

TWO:  If the amp is NOT bridgeable then you can hook the sub to one channel or the other but there is no practical way to drive one voice coil with two amplifiers.

THREE:  If the sub has DVC (Dual Voice Coil) you can connect each coil to the stereo amp left and right outputs.  Make sure you are driving them with the same gain settings in each amp.

Let me know if you have further questions.
C




---------- FOLLOW-UP ----------

QUESTION: Thanks! I have found schematics on the internet which are suppost to do the job. Can you advise on these?

http://allenk.home.infionline.net/techref/splitter.gif

http://www.talkingelectronics.com/projects/Spy%20Circuits/images/StereoToMono.jp

Will these work with powered outputs or not work at all? Otherwise I may have to find something to do with one of the channel (like put the power back into the battery!) as I have already purchased a woofer that is non dual coil and don't want to go into the expense of buying other parts.

ANSWER: There is nothing wrong with letting one channel run idle.  When there is no signal into it and not load at the output the current is very little and draws virtually no power from the car system.

The examples you gave for converting stereo to mono have nothing to do with combining power; the first example is for 600 ohm line feed systems and the second is a small signal circuit and has not speaker output.

My previous recommendation remains.  Use one channel of the amp and let the other remain idle.

C



---------- FOLLOW-UP ----------

QUESTION: i think I will resort to this. One more for safety if ok - should I leave one channel unplugged completely (as in no cables going into it) or complete the loop by connecting the + and - together (I have a feeling that the latter is not the best of ideas!)

thanks!

Answer
Just leave it totally unplugged.  If you short the + and - together it could damage the amplifier.  It would be good to put a shorting plug at the input.  Take an rca plug with a shorting link soldered into it. This will keep spurious noised from entering into the input.  I think you can buy a shorted rca plug at Radio Shack - or make one yourself if you have a soldering iron.
Home made one:

http://www.darrenriley.com/images/324039sm.jpg

Store bought one:

http://www.chemical-records.co.uk/stk_img_thb/A/L/4/AL4396.JPG


Good Luck,
C